Has the nubmber of species increased or decreased throughout time?

The number of species has fluctuated throughout time, undergoing periods of both increase and decrease. There have been several mass extinction events in Earth's history, where a significant proportion of species have become extinct in a relatively short period of time. These extinctions have resulted in a sudden decrease in the number of species.

However, over the course of the planet's history, there has been a gradual increase in the total number of species through a process known as speciation. Speciation occurs when a new species is formed from an existing one through evolutionary divergence. This process has been ongoing for billions of years, resulting in the accumulation and diversification of different species into various forms of life.

Therefore, while there have been periods of species decline due to mass extinctions, the long-term trend over billions of years has been an increase in the overall number of species through the process of speciation.